The long term goal of the proposed investigations is to understand peptide neurotransmitter mechanisms underlying modulation of neuronal activity and regulation of autonomic functions and behavior. We are using as an example the marine mollusk Aplysia which permits detailed analysis of mechanisms at the cellular and molecular levels. Studies done mainly in our laboratory have established that the neuroendocrine bag cells are a multitransmitter system that release 4 peptides derived from a common precursor protein. The peptides serve to modulate activity in neurons located near them in the central nervous system and in the bag themselves. These modulatory effects can last for up to several hours and are thought to regulate visceromotor and behavioral changes that occur during a complex, genetically predetermined behavior, egg laying. One effect of the bag cells is to inhibit certain identified target neurons for more than two hours. We recently purified and partially characterized a novel peptide from the abdominal ganglion that mimics this prolonged inhibition. Partial amino acid sequence analysis suggests the peptide is homologous to a vertebrate brain-gut peptide family. Two other novel neuropeptides have also been isolated and partially characterized. We plan to use biochemical, recombinant DNA and immunocytochemical techniques to further define the molecular basis of the functions of these neuropeptides. We will use recombinant DNA techniques to isolate and sequence the gene coding for the inhibitory peptide. We also plan to determine whether the peptide is released from neurons and to describe the distribution of the peptide within the central nervous system. Similar investigations are planned for the two other novel neuropeptides. The proposed investigations, combined with ongoing functional and behavioral studies, may result in a clearer understanding of fundamental mechanisms of chemical signalling between neurons, the evolution of neuropeptide structure and function, and the cellular basis of genetically predetermined, or "instinctive", behaviors.